Glass for cathode-ray tubes for television display

ABSTRACT

A GLASS ESPECIALLY SUITABLE FOR THE WINDOW OF A CATHODERAY TUBE FOR DISPLAYING COLOR TELEVISION IMAGES WHICH IS SUBSTANTIALLY OPAQUE TO X-RADIATION, NON-DISCOLORING UNDER ELECTRON BOMBARDMENT, AND WHICH CAN WITHSTAND HIGH SEALLING TEMPERATURES. THIS GLASS CONTAINS IN ADDITION TO SILICA, BARIUM AND CALCIU OXIDE, SODIUM AND POTASSIUM OXIDES, ARSENCI AND ANTIMONY OXIDES, AND CERIUN OXIDE. THE AMOUNTS OF BARIUM AND POTASSIUM OXIDES ARE SUCH AS TO INSURE THAT GLASS HAS A SUITABLE COEFFICIENT OF EXPANSION AND TEMPERATURE DIFFERENCES BETWEEN ITS SOFTENING POINT AND ANNEALING POINT.

Us; or 196- 52 Patented 5 3,794,502 auxiliary glass pane in front of thewindow. This disad- GLASS FOR CATHODIsl-RAY TUBES FOR vantagealsoapplies to an implosion resistant cathode- TELEVISION DISPLQY a raytube. In this latter cathode-ray tube a layer of syn- .coem'ahd M vGmuW,Emmasmgel Emdhoven! thetic resinous material which preferably containsglass gggifw sh p l i i s fibers covers in an adhesive manner at leastthe region 7 a of the outer surface which has the strongest curvature iws i ii iiii i s iivgi 'i'iiis gfiii ti ii and isadjacent'thedisplaysurface, leaving the display .1971 s is 11 25 1 surface itselfuncovered. Due to the absence of the laims priority, applicationNetherlands, July 9, 1966, risk of implosion, this tube is suitable tobe incorporated 6609666 i b in a cabinet without using an auxiliaryfront glass pane Int. Cl. cos 3/04 provided the absorption ofX-radiation by the glass of v1 Claim the window is high enough. e

' A principal object of the invention is to provide glass "suitable fora cathode-ray tube window having a suf- ABSTRACT OF THE DISCLOSURE 15'ficiently high absorption of X-radiation.

A e s p i y Suitable f hew n w of ca A further object of the inventionis to provide a glass y tube for d pl yi c0101" televisiQh images wh shis for a cathode-ray tube envelope which will not discolor substantiallyopaque to X-radiation, non-discoloring pnder l mb b d under electronbombardm t, an i h 9 Withstand A still further object of the inventionis to provide a high sealing temperatures. This glass contains in adglass suitable for a cathode-ray tube for color display tion 10 h sbarium nd hi h Sodium an which can withstand high sealing temperatures.Potassium Oxides, s n and i imy i n 1- These and further objects of theinvention will appear --.um oxide. The amounts of barium and potassiumoxides 'as the spooinoanon progresses,

are such asto insure that this glass has a suitable CO- In accordancewith the invention, it has been found fii ien OfeXPanSiOII andtemperature dilferencesjbethat glasses within the range of compositionshereinbetween its softening point and annealing point. 7 v low specifiedmeet these requirements and are highly suitable for' the purposes of theinvention. It should be observed, too, that even minor departures fromthe ranges This s io is a c i n t' t application of the constituents mayresult in a glass which is unsatis- 9' 3 July 1967 WY abandonedfactoryin' one or more respects.

- This invention relates to glass for envelopes of cathode- First,however, in order to obtain a relative measure tubes for televisiondisplay, notably glass for the of the absorption of X-radiation byglass, the absorption Windows of the i of X-radiation of a certainintensity by an arbitrary Particular requirements are imposed uponaglass for glass is compared to the absorption by a known f chi/619E165of i 'f tubes for color televlslonenceglass."To this end, the intensityof the X-radiation Play compansol? wlth glass f l tubes isme'asuredwhich passes through a plate 11 mm. in for the display of blackan'd-whit'e television .This is conthicknessv made f the reference glasswhich is placed hecied With the following diiieiehces the mahliiachll'ean front of an X-ray tube operating at a voltage of 27.5 and of theseiubes- First glass Components kv. These values for the voltage and thethickness of the of envelopes forqelor d pl y cannot be sealed together40 glass are' commonly used for color television display directly as 13Possible Wlih envelopes 9 a kn tubes. Subsequently the voltage of theX-ray tube at p y hilt h -hf? J'OiHefiQIISiHE'aII shill-i161 which;which a plate made of the unknown glass provides an i h y P s into thevltreous'crystaulhe state dill" equal intensity of transmittedX-radiation' is determined. mg Seailhg- This is because a tube for colordisPiay coli- The difference between the last-mentioned voltage and minea SO-Ca d Shadow mask Which determines the 4-5 27.5 kv. is a-relativemeasure of the X-ray absorption paths of the required three electronbeams. Further, the. of the unknown glass. It has been fo nd h h i innerside of the screen is covered with an extremely fiuence of a protectiveauxiliary front glass pane made fine raster-like pattern of threedifferent luminescent subof glass of the usual and usual thickness (3.3mm.) upon stances which corresponds to the apertures of the shadow the Yabsorption is equivalent to kV- This m ans mask, The requirements withregard to the maximum that for USB Of cathode-ray tllbES for C0101display Withdeformation permissible for the glass are therefore much outa Protective fiohi gihss there is need of glass having more stringent inthis case n f a glass intended a value for A kv. which 1s at least +1.5kv. as compared to that of the known glass.

It has also been found that discoloration of glass by the influence ofthe electron bombardment is determined to a considerable extent by theelectrical resistance of the glass insofar as only few or no readilyreducible metals,

for a cathode-ray tube for black-and-white display. Fur thermore, thetemperature to which the tube must be heated during exhaustion andsealing oil must be approximately twenty degrees higher and the heatingproc- 685 15 of a longer duration than h for tubes for such as lead, arepresent in the glass. The previously mencathode'ray tubes forblackfand'whltfi Y' tioned known glasses for color television displaytubes Known glasses are technically entirely satlsfaciory wlth exhibit aslight discoloration; they have a resistivity of apregard to theSoftening Point, the q y and the thermal proximately 10 ohms cm. at 250C. and approximately coeflicient of expansion. However, the absorptionof the 10 -0 h t 350 (3, Experience h shown h y Prodilchd duringOperating (hie the electron glasses for color television display tubesmust have arebombardment of the glass is not high enough, so thatsistivity which is certainly not lower than the specified alone for thisreason it would be necessary to use an values.

pendence of the viscosity not 'be unduly high. In practice,

this" implies that the temperature ditfer'encebetweem'the' softeningpoint, i.e. the temperature at which -th'e viscosity of the glass is-l'poises, and the annealing point, i.e. the temperature at which theviscosity of the glass is:

10 poises, must be at least 195 C.

In connection withusual manufacturing techniques and the very stringentrequirement imposedupon the maximum deformation permissible for theglass components during the manufacture of the tube it is necessary thata glass intended for a color display tube have an annealing point whichis not lower than 485 C. I .7;

Finally, it is important, that a glassfor a color television displaytube have the same coefficient. of expansion as known glasses"(approximately 99 10-" between 30 C. and 300 C.) so as to conform withthe existing glass and metal components which have to be sealed on andinto the tube. -i

Glasses, according to the invention, which meet the aforesaidrequirements, have a composition as follows:

Percent by weight SiO 62-66 Li O 0-1 Na o 78. K 0 65-9 0.10 2-4.5 BaO11-14 MgO 0-3 PbO 0-3 A1 0 1-4 As O -l-Sb O 0.3-0.7 ceo 0.0s-0.3

The softening point of these glasses lies between 680? C. and 700 C.;their annealing point lies between 485 C. and 500 C. and their thermalcoefiicient of expansion is approximately 97 to 100x10 between 30 C. and300 C. The above-mentioned value for A kv. is at least +1.5 kv. andtheir electrical resistance is at least ohm cm. at 250 C. and at least10' ohm cm. at 350 C.

The table below shows, by way of example, six glasses which lie withinthe composition range according to the invention. These glasses areobtained in a manner as is usual in the glass industry by melting theoxides, or compounds which are converted into these oxides during theprocess. i

The essential physical properties are shOWn in the table; U.C. is thecoeflicient of expansion between 30 C. and 300 C.; AP is the annealingpoint; SfP is the softening point; StP is the main point, i.e., thepoint at which the viscosity is 10 poises; WP is the temperature atwhich the viscosity is 10 poises and p is the resistivity in ohmcm.

Composition in percent by weight 62. 6 65.6 64. 5 64. 7 63. 6 65. 5 L 0.5 0. 4 8.4 7.2 7.8 7.5 7.8 7.0 7.3 7.8 6.9 8.4 8.1 8.6 2. 8 4. 2 4. 0 2.5 3. 2 2. 4 2. 0 1. 1 12.7 11. 5 13. 1 13. 7. 12. 4 12. 4 0.5 1.2 1.7 3.4 2.0 2. 5 1. 6 2. 8 1. 5 0. 6 0. 1 0. 6 0.4 0. 4 0. 4 0.3 0.2 0.2 0.2.0.3 0.2 0.1 0.3 0.3 A kv +2. 05 +2. 25 +2. 1 +2. 3 +3. 1 +3. 9 U.C. (X10*") 99. 0 99. 3 99. 7 100. 0 99.0 99. 0 StP C.) 474 459 460 467 645455 AP C) 501 485 486 494 493 485 St? C 689 680 682 691 694 684 WPC.) 1. 006 1. 009 1 008 1. 035. 1 063 1 028 Log- 250 0-.-- 9. 1 10. 0 9.2 9. 1 9. 0 9.1

Log p350 O a 7. 2 7. 8 7. 2 7. 2 7. 1

What is claimed'i s:

1. A glass for the envelope of a "cathode-ray tube for televisiondisplay which does not discolor under electron bombardment, has atemperature coeflicient of expansion of about 99 10-" between 30 and 300C., arr annealing point of at least 485 C., and a softening point atleast C. higher, said glass consisting essentially of:

Percent by weight Si0 62-66 Li O 0-1 Na O 7-8.5 K 0 6.5-9 CaO 2-4.5

BaO 11-14 MgO 0-3 A1203 1-4 As O +Sb O -4 0.3-0.7 Ce0 0.05-0.3 PbO 0-3References Cited UNITED-STATES PATENTS 2,676,109 4/1954 Barnes et a1.10652 3,222,206 12/ 1965 Cornelissen et al. 10652 X FOREIGN PATENTS764,575 7 12/1956 Great Britain 1O6--52 OTHER REFERENCES L. DEWAYNERUTLEDGE, Primary Examiner W. R. SAT'TERFIELD, Assistant Examiner Us.01. X.R. 10653; 313-21s 5 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Iatent No. '3, 794,502 Dated February 26, 1974 Inventor)COENRAAD MARIA LA GROUW I It is certified that error appears in theabove-identified patent v and that said Letters Patent are herebycorrected as shown below:

n Column 4 Qf the Patent:

column 5, line 15 of "Composition in percent by weight" "645" should be--465- Signed nnd'sealed this 5th day of November 1974.

Attest:

. McCOY M'I GIBSONBR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents

